In hot strip rolling and hot plate rolling, cooling water is generally poured onto the material being rolled of a metallic material to control the temperature thereof to a given target temperature. Also, since rolling rolls and table rolls for conveyance come into contact with the material being rolled having a high temperature of about 1000° C., the rolling rolls and the table rolls are generally cooled with cooling water. The cooling water in the latter case is used not only when a high-temperature material is rolled in hot strip rolling and hot plate rolling but also when an ordinary-temperature material being rolled is rolled, for example, in cold rolling.
A rolling plant is provided with a circulation path for cooling water, and the cooling water is frequently used after being pumped up once into a tank at a high place. To move the water, a pump, an electric motor for driving the pump, and a driving device for the electric motor are always used. Therefore, if the circulation of water can be reduced, the energy required for driving the pump can be saved.
For example, Patent Literature 1 (Japanese Patent Laid-Open No. 2006-272339) “Method and Device for Cooling Rolling Roll” discloses a method in which a pump for sending cooling water is operated at a low speed when a material being rolled is absent.